In the interests of fuel economy, there is an increasing drive within the automotive industry towards weight reduction of the component parts of vehicles. However, the weight reduction needs to be achieved without compromising the necessary strength or robustness of the components and, preferably, without increasing material costs or manufacturing costs.
A vehicle wheel bearing is an example of an automotive component where weight reduction is desirable, also in view of the fact that the wheel end bearings belong to the unsprung weight of a vehicle. Raceways of the bearings need to be made from a material of sufficient hardness in order to withstand the stresses of rolling contact. Titanium and certain ceramics are materials that possess the necessary mechanical properties and are also low in weight. They are also expensive and, consequently, bearing steel is more commonly used. Bearing steels have excellent hardenability but cannot be viewed as lightweight materials. Thus, one solution for obtaining a wheel bearing that is relatively cheap to manufacture and reduced in weight is to form the race part of a bearing ring from bearing steel and to form further parts of the ring from a lightweight material.
In U.S. Pat. No. 6,485,188, a wheel mounting with a bearing race embedded in a cast component is suggested. In one embodiment, the wheel mounting is a hub in which an outer bearing race made from a bearing grade steel is embedded in a cast component that has a radial flange for the attachment of a vehicle wheel. In a further embodiment, the wheel mounting is a steering knuckle that is cast around the outer bearing race. Suggested metals for the cast component are steel, ductile iron and aluminium. After the step of casting, the outer raceways of the bearing race are induction hardened.
There is still room for improvement, however, in terms of simplifying the manufacture a bearing ring comprising a cast or overmoulded part and in terms of realizing a bearing unit comprising such a bearing ring, which is capable of delivering the same mechanical and structural performance as a conventional unit made entirely from e.g. a bearing steel.